The present invention relates to a process for the conversion of 1,4 butynediol to 1,4 butenediol by selective liquid phase hydrogenation. More particularly, the present invention relates to a process for the conversion of 1,4 butynediol to 1,4 butenediol in a basic medium using a novel noble metal containing catalyst.
1,4 butenediol is a useful intermediate in the production of pesticide, insecticide and vitamin B6. Being an unsaturated diol it can be used in the synthesis of many organic products such as tetrahydrofuran, n-methyl pyrrolidione, xcex3-butyrolactone, etc. It is also used as an additive in the paper industry, as a stabiliser in resin manufacture, as a lubricant for bearing systems and in the synthesis of allyl phosphates.
Prior art discloses the use of a number of catalysts for the manufacture of 1,4 butenediol by the hydrogenation of 1,4 butynediol. Most of the prior art patents are based on a combination of palladium with one or more mixed compounds of copper, zinc, calcium, cadmium, lead, alumina, mercury, tellurium, gallium, etc. GB A 871804 describes the selective hydrogenation of acetylinic compound in a suspension method using a Pd catalyst which has been treated with the salt solutions of Zn, Cd, Hg, Ga, Th, In, or Ga. The process is carried out at milder conditions with 97% selectivity for cis 1,2-butenediol and 3% to the trans form. Moreover, use of organic amines have been suggested as promoters in the catalyst system.
U.S. Pat. No. 2,681,938 discloses the use of a Lindlar catalyst (lead doped Pd catalyst), for the selective hydrogenation of acetylinic compounds. The drawback of this process is the use of additional amines such as pyridine to obtain good selectivity for 1,4 butenediol.
German patent DE 1, 213, 839 describes a Pd catalyst doped with Zn salts and ammonia for the partial hydrogenation of acetylinic compounds. However, this catalyst suffers from the drawback of short lifetime due to poisoning.
German patent application DE A 2, 619, 660 describes the use of Pd/Al2O3 catalyst that has been treated with carbon monoxide for the hydrogenation of butynediol in an inert solvent. The disadvantage of this catalyst is that is treated with carbon monoxide gas which is highly toxic and difficult to handle.
U.S. Pat. No. 2,961,471 discloses a Raney nickel catalyst useful for the partial hydrogenation of 1,4 butynediol. The catalyst of this process gives a low selectivity for 1,4 butenediol. Another U.S. Pat. No. 2,953,604 describes a Pd containing charcoal and copper catalyst for the reduction of 1,4 butynediol to 1,4 butenediol with 41% selectivity for 1,4 butenediol. However, this process results in the formation of a large number of side products and is therefore undesirable.
U.S. Pat. No. 4,001,344 discloses the use of palladium mixed with xcex3-Al2O3 along with both zinc and cadmium or either zinc or cadmium together with bismuth or tellurium at 65xc2x0 C. to 72xc2x0 C. and 4-12.5 bars hydrogen pressure for the preparation of 1,4 butenediol by the selective hydrogenation of 1,4 butynediol. However, a large number of residues are formed (7.5-12%) which lowers the selectivity of 1,4 butenediol to 88%.
U.S. Pat. Nos. 5,521,139 and 5,728,900 describes the use of a Pd containing catalyst for the hydrogenation of 1,4 butynediol to prepare 1,4 butenediol. The catalyst used is a fixed bed catalyst prepared by applying Pd and Pb or Pd and Cd successively by vapor deposition or sputtering to a metal gauze or a metal foil acting as a support. In this process also the selectivity obtained for cis 1,4 butenediol is 98%. The disadvantage of this process is that a trans butenediol with residues are also obtained.
All the above catalysts for the hydrogenation of butynediol to butenediol suffer from disadvantages such as they contain more than two metals along with other promoters such as organic amines. Their preparation becomes cumbersome and all the reported catalysts do not give complete selectivity for the desired product 1,4 butenediol. The formation of side products and residues have also been reported which affect the efficiency of the process and the recovery of pure 1,4 butenediol is difficult. Another disadvantage that prior art catalysts suffer from is short life due to fast deactivation.
The prior art literature shows that the catalysts used for the hydrogenation of 1,4 butynediol are mainly palladium or nickel based catalysts. There is no disclosure or report on the use of platinum based catalysts or catalysts containing a combination of palladium and nickel for the hydrogenation of 1,4 butynediol to prepare 1,4 butenediol.
It is therefore important to obtain and/or develop catalysts that overcome the disadvantages of prior art catalysts used in the hydrogenation of 1,4 butynediol to 1,4 butenediol enumerated above.
The main object of the invention is to provide a process for the preparation of 1,4 butenediol by the hydrogenation of 1,4 butynediol that is cheap and efficient.
It is another object of the invention to provide a process for the preparation of 1,4 butenediol with 100% selectivity.
It is another object of the invention to provide a process for the conversion of 1,4 butynediol to 1,4 butenediol using a noble metal catalyst that optionally contains nickel, on a suitable support, under mild reaction conditions without poisoning.
It is a further object of the invention to provide a process for the conversion of 1,4 butynediol to 1,4 butendiol that shows 100% selectivity for the production of cis 1,4 butenediol.
It is a further object of the invention to provide a process for the conversion of 1,4 butynediol to 1,4 butenediol that uses a stable catalyst that is capable of being recycled a number of times without losing its activity and selectivity.
It is another object of the invention to provide a process for the preparation of 1,4 butendiol with 100% selectivity for the production of cis 1,4 butenediol by mere separation of the catalyst.
Accordingly the present invention relates to a process for the preparation of 1,4 butenediol comprising hydrogenation of an aqueous solution of 1,4 butynediol under stirring conditions, over a supported platinum, palladium and nickel catalyst in basic medium at a temperature in the range of 20-110xc2x0 C. and H2 pressure in the range between 200-700 psig till the reaction is completed, cooling the reaction mixture to room temperature and separating the catalyst by known methods to obtain 1,4 butenediol.
In one embodiment of the invention, the concentration of 1,4 butynediol in aqueous medium is in the range of 10-50%.
In another embodiment of the invention, the pH of the reaction mixture is maintained in the range of 8-10 by adding a base such as ammonia.
In a further embodiment of the invention, the temperature of the reaction is preferably in the range of 30-90xc2x0 C.
In yet another embodiment of the invention, the catalyst is recycled 10 times without losing its activity or selectivity and the turn over number (TON) is 4xc3x97103hxe2x88x921.
In yet another embodiment of the invention, the catalyst is of the general formula AB(y)C(z) wherein A is a support comprising of carbonate of calcium or zeolite, B is platinum or palladium, y=0.2 to 10%, C is nickel and z=0 to 15.0%, with the proviso that when B is Pt, z=0.
In the present invention the catalyst is prepared by impregnating palladium or platinum precursor with support (such as CaCO3, MgCO3, BaCO3, or NH4xe2x80x94ZSM 5) in a basic medium (pH=7-12), stirred in water and heated in the temperature range of 60-120xc2x0 C., preferably 70-90xc2x0 C. The mixture is then reduced by adding a conventional reducing agent such as formaldehyde. The solution is stirred, filtered, washed and dried at a temperature in the range of 100-250xc2x0 C., preferably 140-200xc2x0 C. in static air for a period in the range of 5-12 hours.
The hydrogenation catalyst used in the process of the invention is of the general formula AB(y)C(z) wherein A is a support comprising of a salt of a Group II A metal or zeolite, B is a noble metal, y=0.2 to 10%, C is nickel and z=0 to 15.0% with the proviso that when B is Pt, z=0.
The hydrogenation catalyst of the general formula AB(y)C(z) wherein A is a support comprising of a salt of a Group II A metal or zeolite, B is Pd or Pt, y=0.2 to 10%, C is nickel and z=0 to 15.0% with the proviso that when B is Pt, z=0, is prepared by:
i. dissolving a Pd or Pt precursor in a mineral acid by stirring at a temperature in the range between 60xc2x0 C. to 120xc2x0 C.;
ii. diluting the above solution by adding water;
iii. adjusting the pH of the solution to the range of 8-12 by adding a base;
iv. adding a support to the above solution;
v. heating the mixture to a temperature in the range of 60xc2x0 C. to 120xc2x0 C.;
vi. reducing the above mixture using a conventional reducing agent;
vii. separating the catalyst formed by any conventional method;
viii. washing and drying the product to obtain the said catalyst.
The catalyst may optionally have a combination of Pd with nickel. When the noble metal comprises of palladium and z=0.2 to 15%, the catalyst obtained at the end of step viii above is mixed with a solution of nickel in a basic medium having a pH in the range of 8-12, the mixture stirred for about 1 hour and the catalyst separated by any conventional method. The catalyst is then dried at about 150xc2x0 C. up to 10 hours in static air, reduced at a temperature in the range of between 390-420xc2x0 C. for a time period in the range of between 5-12 hours in a flow of hydrogen, the reduced catalyst is then separated by any conventional method and washed and dried to obtain the final catalyst containing palladium and nickel.
The source of Pd or Pt is a salt of Pd or Pt selected from the group consisting of acetate, bromide, and chloride and the source of nickel is a salt of nickel selected from the group consisting of acetate, carbonate, chloride and nitrate.
The support is a Group II A metal salt selected from the group consisting of acetates, nitrates, chlorides and carbonates of magnesium, calcium and barium and the source of zeolite is NH4xe2x80x94ZSM5.
The base used may be selected from the group consisting of sodium carbonate, potassium carbonate, potassium hydroxide, and sodium hydroxide.
The reducing agent used in the preparation of the catalyst is selected from the group consisting of hydrazine hydrate, hydrogen containing gas, and formaldehyde.
The catalyst prepared as per the procedure described below in the examples can be reduced in a muffle furnace at 400xc2x0 C. in hydrogen flow for a time period ranging between 5-12 hours, preferably 7 hours.
In a feature of the invention, high purity 1,4 butenediol can be simply obtained by the removal of the catalyst from the product stream. The selectivity of the process at milder process conditions is 100%.
The present invention achieves 100% conversion of 1,4 butynediol with 100% selectivity for cis 1,4 butenediol at mild process conditions. At higher temperatures, while 1,4 butynediol is converted completely, the selectivity for cis 1,4 butenediol is less, generally xe2x89xa690%. The formation of side products such as acetals, xcex3-hydroxybutaraldehyde, butanol at higher temperatures is also more pronounced.
Hydrogenation of 1,4 butynediol is carried out in an autoclave under stirring conditions in the presence of a Pd or Pt containing catalyst suspended in a mixture of 1,4 butynediol in water at temperature and pressure conditions as given in the examples. The mixture is made alkaline (pH=8-12), by the addition of base such as ammonia. Before pressurising the autoclave, it is ensured that there is no air present inside the autoclave. The hydrogenation is complete when the absorption of hydrogen is stopped or unchanged. After the reaction is complete, the reactor is cooled to ambient temperature and the contents discharged and analysed using a gas chromatograph.